Ozone is a naturally occurring allotrope of oxygen, specifically O.sub.3, as opposed to the more usual form of oxygen, O.sub.2. It has been known and used for many years as a disinfectant and oxidant, particularly in water sterilization and in the food service industries. Ozone kills all species of dangerous food bacteria rapidly. When dissolved in water, ozone exhibits biocidal qualities at concentrations below 0.5 parts per million. In aqueous solution it is capable of disinfecting food in less than a minute at concentrations of only 0.10 mg/liter, and much faster at higher concentrations. By contrast, chlorine requires more than an hour at concentrations of 1.0 mg/liter to accomplish the same level of sanitization. Moreover, ozone imparts no taste or odor to foods, and helps to maintain healthy and attractive coloring. Nor does ozone create harmful byproducts in sanitizing, in as much as it breaks down to molecular oxygen after sanitizing reactions. Chlorine creates many undesirable and/or toxic organo-chloro compounds, and leaves undesirable tastes and odors in foods. For the same reasons, ozonated water is superior for use in ice machines, potable water production, swimming pools, hospitals and medical laboratories, fishing vessels, ships, military applications, and waste destruction.
Commercially, ozone is generated by a number of means, but most typically in the electrical field of a corona when relatively large quantities of the substance are desired. Ozone is not a stable compound, possessing a half-life which is affected by several factors, including temperature, pressure, light, or the presence of any other material which will function as a reducing agent, i.e., a source of electrons. The substance is more stable at low temperatures and when placed in uncontaminated aqueous solutions, etc. Copious data is available anent ozone in any handbook of Chemistry and Physics, as well as many other sources. The International Ozone Association is a particularly good source for information on Ozone.
One of the safest and most convenient means for using ozone as a disinfectant or sterilizer of food and the like has been to force it into solution in water, and to use the resultant aqueous solution to wash the food, etc. Aprincipal limitation to this use of ozone, however, has been the difficulty of providing ozonated water on a selectably continuous, intermittent, or demand basis. This is due at least partly to difficulties in handling gaseous ozone and storing ozonated water, and also supplying relatively smaller quantities of ozonated water. To do so it is found to be very advantageous to allow for the selectively continuous recirculation of previously-ozonated water through the ozonating apparatus, so that the selective removal of arbitrary amounts of ozonated water is immediately compensated by the introduction of fresh water for ozonation and so that the remaining previously-ozonated water can be maintained at the highest possible or suitable level of ozonation. Yet ozone, particularly in its gaseous form, can be highly corrosive with some materials. In solution, it can be corrosive and/or passivating, depending upon the particular material. It is typically the case (traditionally) that water to which ozone is added does not return to the point in a system where ozone was injected. Specifically, this is to say that ozonated water is not recirculated in a closed loop, especially where the recirculated water is continuously re-ozonated. This is due to problems of corrosion, materials compatibility problems, and the absence of need to return ozonated water to the point where ozone was injected. However, and especially where relatively small quantities of ozonated water are desired, it is advantageous, albeit difficult, to provide closed loop recirculation with continuous or intermittent withdrawal of the ozonated water product. This difficulty has been especially vexing where relatively small quantities of ozonated water are required, but on a substantially continuous basis, such as the feed of ozonated water to ice machines, surgical wash stations, small washing operations, waste destruction, disinfecting seafood, poultry, produce, etc.
Several attempts at providing ozonated water for sterilization or disinfectant use have been made, but none is optimized for the effective, economical, and efficient solution of problems associated with the continuous or intermittent supply of ozonated water, particularly where relatively small amounts are desired, through the use of continuous recirculation or feed back loops in systems operating at low pressures. For example, U.S. Pat. No. 5,585,003 to Van Newenhizen discloses method and apparatus for treatment of feedwater for use in dialysis by means of ultraviolet radiation and ozonation. Like many attempts at sterilization through the use of ozonated water, however, the Van Newenhizen method relies on the use of bubble column diffusers, which are inefficient devices for entraining ozone in water. The efficiency of the Van Newenhizen device also suffers through its requirement for means for actively monitoring the water level within the system, and for replacing water withdrawn for use after ozonation. Moreover, due to its sole intended purpose of providing purified water for dialysis, the Van Newenhizen system is adapted for the ozonation of water treated by deionization or reverse osmosis processes only. For most day to day drinking and sterilization applications, it is advantageous for an ozonation system to be compatible with any type of water or liquid.
U.S. Pat. No. 5,352,369 to Heinig, Jr.; U.S. Pat. No. 5,364,537 to Paillard; U.S. Pat. No. 5,415,786 to Martin et al.; U.S. Pat. No. 5,433,866 to Hoppe et al.; U.S. Pat. No. 5,514,284 to Uban et al.; and U.S. Pat. No. 5,709,799 to Englehard all describe apparatus for the continuous production of relatively large amounts of ozonated water by means of open water cycles: water is taken in, treated, and discharged without further cycling through the ozonation apparatus. For relatively smaller applications, and in some large-scale production applications, the use of closed-loop recirculation systems has been found to be more efficient.
U.S. Pat. No. 5,336,413 to van Staveren discloses process and apparatus for the purification of water by injection of oxygen, ozone, and other compounds. The van Staveren device is relatively complex, involving multiple chemical reactors and a number of pumps to santize water under pressures as high as 16-20 bars and recycling of treated water through various filtration stages.
U.S. Pat. No. 5,683,576 to Olsen discloses water ozonation treatment apparatus having limited recirculation capability for water which has become contaminated within the system. However, recirculation of ozonated water is not continuous, and the Olsen apparatus is incapable of dispensing water while recirculation is taking place. Moreover, activation and monitoring of the recirculation cycle requires a microcomputer or other microcontroller.
Thus there is a need for efficient, effective, and economical means for producing ozonated water on a selectively continuous or intermittent basis.